Rosaceæ. 85 



in Rub. chamæmorus, differences which are connected with differ- 

 ences of life-duration and function. The conducting tissue ex- 

 hibits the greatest differences. In the aerial shoot there are 

 about 10 primary bundles separated by narrow medullary 

 rays which remain in their primary condition; the intraf as- 

 cicular cambium forms only a small amoimt of wood. I 

 have not been able to see any endodermis in the aerial shoots, 

 though such is distinctly seen in the wandering shoots. In 

 the latter a continuous cambium begins to function very 

 early and a considerable amount of wood is formed contain- 

 ing numerous medullary rays which are usually one cell- 

 layer broad. In older rhizomes more or less distinct annual 

 rings occur; the oldest I have seen were, however, only three 

 years old. As regards the proportion between the diameter 

 of the pith and that of the whole organ, the usual difference 

 obtains between aerial and under-ground shoots; the propor- 

 tion in the aerial shoot is larger (about ^) than in the 

 runners measured in their primary condition (i — f). In 

 addition there is found in the aerial shoot, but not in the 

 runners, a fairly thick fibrous tissue outside the phloem, 

 and the outermost cortical layer is somewhat collenchymat- 

 ous. The cortex in the runners is considerably thicker than 

 in the aerial shoot, but more space is not thereby gained 

 for reserve food-material, because even in the first vegeta- 

 tion-period of the shoot a periderm is formed in the outer- 

 most layer of the pericycle. Then the cortex collapses and 

 persists during the following years as a loose brown mantle 

 around the rhizome. But even in the third year the phel- 

 logen has not been able to form more than 3 — 4 layers of which 

 the outer have become corky. In the aerial stem no periderm 

 is developed, not even so much as in Rub. arcticus (Fig. 36, i*') ; 

 consequently, the structure of the assimilatory shoot of Rub. 

 chamæmorus is the simplest among the species of Sect. Cylactis 

 here investigated. — The epidermis around the young runner 



